Gear generating method and apparatus

ABSTRACT

An improvement in gear cutting methods and apparatus of the type in which a multiple-tooth gear is manufactured from a blank by the generation of successive tooth slots by a cutter which makes a plurality of cuts during the generation of each successive slot. The improvement comprises an alteration in the timed relationship between the cutting rate and the generating roll during successive tooth slot cutting operations such that the number of cuts made by the cutter differs from slot to slot. While the effective contours of successive tooth slots generated by this improved method and apparatus are substantially identical, their cutting patterns differ, resulting in substantial reduction in the noise produced by power transmission systems utilizing gears generated in this manner.

United States Patent [151 3,653,290 Hunkeler [4 1 Apr. 4, 1972 541 GEARGENERATING METHOD AND Primary Examiner-Gil Weidenfeld APPARATUSAttorney-Morton A, Polster [5 7] ABSTRACT An improvement in gear cuttingmethods and apparatus of the type in which a multiple-tooth gear ismanufactured from a blank by the generation of successive tooth slots bya cutter which makes a plurality of cuts during the generation of eachsuccessive slot. The improvement comprises an alteration in the timedrelationship between the cutting rate and the generating roll duringsuccessive tooth slot cutting operations such that the number of cutsmade by the cutter differs from slot to slot. While the effectivecontours of successive tooth slots generated by this improved method andapparatus are substantially identical, their cutting patterns differ,resulting in substantial reduction in the noise produced by powertransmission systems utilizing gears generated in this manner.

12 Claims, 6 Drawing Figures [72] inventor: Ernst J. Hunkeler, Fairport,NY.

[73] Assignee: The Gleason Works, Rochester, NY.

[22] Filed: June 29, 1970 [21} Appl. No.: 52,219

[52] US. Cl ..90/5, 90/3 [5 l Int. Cl. .1323 9/10 [58] Field of Search..90/5, 3, 9.4, l

[56] References Cited UNITED STATES PATENTS 2,426,774 9/1947 Jury ..90/53,288,031 11/1966 Krastel et a1 ..90/5

PAIENTEUAPR 4 m2 SHEET 1 OF 3 (H ERNST J. HUNKELER INVENTOR.

FIGURE 2 PA'TE'N'TEDAPR 41972 3.653.290

SHEET 2 or 3 FIGURE 3 ERNST J HUN'K-ELER FIGURE 4 INJVENTOR PATENTEDAPR4 I972 R (CUTS PER REVOLUTION) |23456789|Olll2 so so 9o :20 I50 I80 am240 270 300 330 CAM ROTATION FIGURE 5 FIGURE 6 ERN'STFJ. .H KELER I NVEN TOR.

GEAR GENERATING METHOD AND APPARATUS This invention relates toimprovements in well known methods and apparatus for the cutting ofgears by generation and, more particularly, relates to the production ofgears for use in power transmission systems to achieve a reduction inobjectionable noise produced by such transmissions.

Objectionable noise from gear trains has long been a problem in themanufacture of power transmission systems, particularly with suchsystems as used in automobile transmissions. As is well known in thisart, even exceptionally smooth gear tooth action results in audiblevibrations directly related to the number of teeth on the mating gearsin the train, the objectionable frequencies generally being thoseequivalent to the number of teeth meshing per second, as well asharmonics of these basic frequencies.

It is also well known that some objectionable peaks of gear noise aredirectly related to the flat patterns which result from the cuttingoperation. That is, the curved contours of gear teeth, while appearingrelatively smooth to the unaided eye, are actually formed by a pluralityof very narrow flat areas of varying width, each such flat areacorresponding to the passage of a single cutter blade through the toothslot during generation. Since these cutting patterns are substantiallyidentical on each successive tooth of gears cut by prior art methods,the noise generated by the sliding contact of such gears when run inmesh is repetitive and results in undesirable noise peaks at particularfrequencies.

The cutting-pattern noise just referred to above is further aggravatedby any misalignment or eccentricity of the cutter blades. While suchinaccuracies may be so very slight that gears produced by such cuttersfall well within allowable dimensional tolerances, they still causeunusual variations in the amount of metal each successive blade removesfrom a tooth slot during generation and often result in unusually wideflats" on the surface of the teeth. Since these unusual cutting patternsare substantially identical on each tooth of a gear cut by a slightlymisaligned or eccentric cutter, they often result in unacceptable noiselevels. According to present cutting methods, the first set of gears cuton a machine following its set-up by the operator (or followingreplacement of the cutter head) is generally tested to check for anysuch cutter inaccuracies which might cause cutting patterns which areunusual and result in unacceptable noise in a gear train. In suchevents, the cutters must be re-trued on the machine and/or machineadjustments are made by the operator to correct or compensate for suchinaccuracies. Such special cutter and machine adjustments are extremelycostly in time, particularly on mass production machinery in which aplurality of cutting machines are interconnected by automatic workpieceloading and transfer mechanisms.

The invention herein provides method and apparatus wherebycutting-pattern noise can be substantially reduced, and this importantimprovement reduces normal cutting-pattern noise peaks as well as thoseresulting from cutter inaccuracies. That is, by virtue of the novelmethod and apparatus disclosed herein, the minute variations in thepattern of flats which occur in the surface of gear teeth manufacturedon gear cutting machines will no longer result in the production ofundesirable peaks of unusual frequencies.

In essence, the subject invention prevents such tooth surface patternsfrom occuring in a repetitive manner on successive teeth cut on the samemachine. This remarkable and important result is produced in anextremely simple manner, namely, by varying the timed relationshipbetween the cutting rate at which the cutter moves relative to the speedof the generating roll during generation of successive tooth slots. Itwill be appreciated by those skilled in this art that the number of tinyflat areas which comprise the surface of any particular gear tooth is indirect relation to the number of revolutions the cutter head makesrelative to the workpiece blank during each generating roll. Therefore,according to the subject invention, by changing the timed relationshipbetween the rate at which the cutter turns and the speed of thegenerating roll for each successive tooth slot, different numbers ofcuts occur during the generation of each such successive tooth in thegear. In this way, cutting patterns which heretofore appeared at thesame relative position on each successive tooth (by virtue of therepetitive generating cycle and the constant relationship between cutterrate and generating roll) now are positioned in a random manner fromtooth to tooth. This random positioning of the cutting flats preventsthe production of undesirable peak noise frequencies when these gearsare used in power transmissions.

It will be especially appreciated by those in the art that the methodand apparatus disclosed herein will provide important savings on massproduction machinery because even in the event of any slight cutterblade eccentricity or misalignment which, as noted above, results inunusual variations in the width of the flat areas forming the contour ofa gear tooth, such variations will not appear at the same place onsuccessive gear teeth due to the alteration of the timed cuttingrelationship. This means that cutters trued off the machine topredetermined tolerances can be mounted on a gear machine withoutrequiring an operator to further adjust the machine or cutter thereafterin order to avoid objectionable cutter-pattern noise peaks, therebyproviding a substantial saving in the cost of mass producingtransmission gears.

According to a further feature of the invention herein, alternation ofthe timed relationship between cutting rate and generating roll for thecutting of successive tooth slots does not change the speed at whichmachine operations occur during the remaining portions of the repetitivecutting cycle. That is, cutter withdrawal, indexing of the work blank,and infeed of the cutter for engagement with the blank to generate thenext successive slot, are all carried out at optimum machine speeds, thenovel relative variations in cutter speed taking place only during thecutting portion of the repetitive cycle.

While it will be appreciated that the method and apparatus disclosedherein are adaptable to other gear generating systems, the inventionwill be described as applied to a spiral bevel gear generating machineusing a face mill cutter.

The foregoing and other objects and advantages of the invention will beapparent from the following description and the accompanying drawings inwhich:

FIG. 1 is a schematic representation of the cutter and work heads of atypical bevel gear generating machine of the type contemplated forimprovement by the invention herein;

FIG. 2 is a partially schematic diagram of a preferred form of steppingmechanism and cam control for varying the timed relationship betweencutting rate and generating roll on a machine such as that generallyillustrated in FIG. 1;

FIGS. 3 and 4 are schematic illustrations of the generation ofsuccessive tooth slots in a work blank, showing the relatively differentcutting patterns effected by the invention herein;

FIG. 5 is a graphic representation of suggested variations in generatingroll speed selected for successive tooth-slot generation by theapparatus shown in FIG. 2; and,

FIG. 6 is a simplified schematic circuit diagram for altering the speedof the machines cycle control motor to provide a desired variation ingenerating roll speed during the cutting portion of a machine cyclewhile permitting the cycle to operate at a predetermined optimum speedduring the remaining portions of the machine cycle.

FIG. 1 illustrates the cutter and work heads of a typical bevel geargenerator of the well known type of gear cutting machinery to which theinvention herein may be applied.

As is well known in this art, such a machine includes a work head 10which receives and holds a gear blank 12 in which a plurality ofspirally shaped teeth are generated by a face mill cutter 14 comprisinga cutter head 16 onto which a plurality of cutter blades 18 are securelyfixed.

Cutter 14 is mounted for rotation about axis 20 in a cradle 22 which inturn is mounted in a cutter slide 24 for rotation about axis 26.

As is well known in this art, generation of spiral bevel gear from workblank 12 is accomplished in the following manner:

shown to comprise a plate 68 which is substantially identical to theplate 56 in the tracer probe assembly 16 and which serves substantiallythe same purpose. Plate 68 is fixed to the lower end of frame member 22and pivotally connected to a motor frame 70 to permit the frame 70 to bedisposed in alignment with member 22 or in either of two angularorientations, as selected by the operator. Suffice it to say that theplate 68 bears the same relation to frame 70 as the plate 56 bears tothe extension 50 and that normally both extension 50 and frame 70 aredisposed in the same relative orientation.

Frame 70 supports a rotary motor 72 which is energizable to rotate acutter 74 depending therefrom. The rotating cutter 74 removes materialfrom the block of pattern stock as it is displaced by the operator,synchronism with the model being obtained by the rigid frame 10.

Considering now the overhead support means 12 in greater detail,reference will be made to FIGS. 1, 5, and 6. Assembly 12 includes ahorizontally disposed longitudinally extending channel 80 havinglongitudinally spaced trolleys 82 and 84 affixed thereto. The trolleys82 and 84 include wheels which are adapted to engage and ride on thelower flange of an l beam 86 which may be part of the building structurewithin which the apparatus is installed. The trolleys 82 and 84 thusserve to permit the frame to be displaced longitudinally along the lbeam 86.

Channel 80 carries at the left end as shown in FIG. 1 a pair of paralleldepending brackets 88 which receive a cylindrical member 90 which, inturn, is telescopically engaged within the vertical frame member 20. Onthe longitudinally opposite end of the channel 80, a second pair ofparallel depending brackets 92 receive a cylindrical member 94 which istelescopically engaged with the vertical frame member 22. The brackets88 and the cylindrical member 90 are provided with horizontally alignedholes which receive a pivot pin 96 to permit the cylindrical member 90and the frame 10 to pivot about a longitudinal axis relative to thebrackets 88. A cotter pin may be used to maintain the pivot pin 96 inplace. A similar pivot pin 98 is provided at the opposite longitudinalend of the frame 10 to maintain the short cylindrical telescopic member94 in engagement with the brackets 92. Accordingly, the entire frame 10may be pivoted or swung about a longitudinal axis passing through pins96 and 98.

It is very important that the longitudinally opposite ends of the frame10 are displaced vertically in unison with one another thereby tomaintain the tracer assembly 16 and the cutter assembly 18 at the samevertical level at all times. To provide this unison verticaldisplacement as well as to counterbalance the mass of the frame 10, apair of longitudinally spaced chains 100 and 102 are affixed to theupper cross member 24 of the frame 10 and extend upwardly over sprockets104 and 106. The sprockets are mounted on longitudinally opposite endsof a rod 108 which interconnects the sprockets 104 and 106 for unisonrotation. Rod 108 passes through suitable bearings to permit thesprockets 104 and 106 and the rod 108 to rotate freely.

Chains 100 and 102 are carried horizontally and transverly back to idlerassemblies from which the chains drop vertically to a counterweight 118.The idler assembly for chain 100 is shown in FIG. 4 to include a supportarm 110 carried by channel 80 and a second sprocket 112. The idlerassembly for chain 102 is identical. The counterweight 118 is preferablyselected .to equal the total suspended mass of the frame 10 so that inthe absence of an input force applied to the frame 10 by an operator,both the frame 10 and the counterweight 118 tend to remain in whateververtical position is previously established by the operator. Since thesprockets 104 and 106 must rotate in unison due to the interconnectingrod 108, and chains 100 and 102 cannot slip on the sprockets, verticaldisplacement of the frame 10 is rectilinear in nature, thus, preservingthe vertical elevational equality as between the tracer assembly 16 andthe cutter assembly 18.

Considering the platform 14 in greater detail, this assembly is shown inFIG. 3 to be fabricated from a substantially rigid and level plywooddeck 120 which is rectangular in overall configuration. Deck 120 ismounted on a quadrangular frame 122 which elevates the deck 120 byapproximately 10 inches. Care is taken to ensure that the surface ofdeck 120 is level such that the vertical distance between the deck andthe probe 46 is equal to the vertical distance between the platform andthe cutter blade 74. Blade 74 may be somewhat higher than probe 46 toleave extra stock on the model. A centerline 124 is drawn on the deck120, this centerline representing the longitudinal displacement path ofthe probe assembly 16 and cutter assembly 18 when the frame 10 isvertically oriented. Care is taken to align the centerline of the modeland the pattern stock with the centerline 124 when these elements areplaced on the deck 120. The alignment between the tracer probe assemblyand the platform centerline 124 may be quickly and easily checked byremoving the tracer probe head 46 from the cylindrical extension andplacing a lead pencil or other suitable marking device in its place,lowering the frame 10 until the pencil engages the deck 120 of theplatform 14 and then longitudinally displacing the frame 10 to determinewhether the newly marked centerline corresponds with the preestablishedcenterline 124.

Although the operation of the illustrative embodiment of the inventionis believed to be apparent from the foregoing structural description, abrief summary of the operation will now be made.

A hard surface model is placed on the deck 120 of the platform 14, thecenterline of the model being aligned with the longitudinal centerline124 of the deck 120 such that the probe head 46 may be displaced overthe surface of the model. The angular orientation between the probe headextension 50 and the vertical member 20 is adjusted to correspond to thenature of the surface to be traced. A block of pattern stock, such aspolystyrene foam, is placed on the deck 120 beneath the cutter assembly18 with the centerline of the block on the centerline 124. At thispoint, the motor 72 is energized to rotate the cutter tool 74. When anordinary router motor is used, the rpm is decreased by means of asuitable transformer type power supply such that the cutter tool 74 isrotated at a much lower speed than the ordinary operating speed of arouter.

The operator then addresses the frame 10 placing himself in a facingrelationship with the A-shaped opening defined by the cross members 42and 44. The operator places his hands on the members 42 and 44 to directthe frame 10 longitudinally, vertically, and pivotally about thelongitudinal axis as necessary. Counterweight 118 permits the frame 10to be raised and lowered by the application of small forces thereto, thechains 100 and 102 and the sprockets 104 and 106 permitting the freevertical adjustment of the frame 10 as previously described. The rod 108interconnecting sprockets 104 and 106 ensures a unison verticaldisplacement of the opposite longitudinal ends of the frame 10, thus tomaintain the tracer probe assembly 16 and the cutter assembly 18 on thesame horizontal level during vertical displacement of the entire frame10. Trolleys 82 and 84 permit the frame 10 to be dis- 7 placed in thelongitudinal direction defined by the l-beam 86 and the pivotalconnections between the brackets 88 and 92 and the telescopic verticalsections and 94 permit the entire frame 10 to be pivoted about alongitudinal axis thereby to accomplish and afford 3 of freedom in themovement of the frame 10 relative to the model and pattern stocksurfaces.

It is to be understood that the invention has been described withreference to an illustrative embodiment and that various modificationsthereof will be apparent to those skilled in the an.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A pattern duplicator comprising: a rigid, manually disv placeableframe including a pair of longitudinally spaced vertical members andmeans rigidly connecting the members, said frame being adapted foroverhead, vertical suspension and having a longitudinal axis, tracermeans depending from the When the cradle reaches the end of itsgenerating roll, the timing cam moves switch 60 to the position shown bythe dotted line, opening with upper contact 62 and closing with lowercontact 64. This thereby changes the control of the speed of motor 56 tothe circuit including potentiometer 66 which is set to a predeterminedvalue by the machine operator. The circuit stays in this condition untilthe machine cycle repeats to the point where another generating roll isready to begin, at which time switch 60 is closed once again with uppercontact 62, and the circuit operation then repeats in the manner justexplained above.

In this way, the non-cutting portion of the machine cycle may becontrolled for optimum operational speeds while still realizing theadvantages of the invention s novel varying rates for the timed relationof the generating roll.

The rather simple invention disclosed above has provided a major advancein gear generation technology by solving a problem which has plagued theindustry since gears have been used in power transmission systems. Bysimple changing the cutting pattern of each successive tooth in agenerated gear (without changing the effective contour of the teethwhich remain substantially identical throughout the gear), it has beenpossible to reduce remarkably the amount of undesirable noise generatedin transmission by such gears.

While only a single embodiment of the invention herein has beendisclosed above, it should be obvious that this has been selected merelyto facilitate explanation of the invention and not to limit the formwhich the invention may take. Many variations, modifications, andalterations of the apparatus disclosed herein may be achieved to carryout the novel method disclosed herein.

What is claimed is:

1. in a method for cutting a multiple-tooth gear from a blank by using awell known repetitive cycle including the steps of:

a. engaging a cutter with the blank while producing a relative rollingmotion therebetween at a predetermined speed to generate a tooth slot inthe blank, and

b. moving the cutter at a predetermined cutting rate in timedrelationship to said generating roll so that the cutter makes aplurality of cuts in the blank during each generating roll,

the improvement comprising the further step of:

c. altering the timed relationship of the cutting rate relative to thespeed of the generating roll between at least two successive tooth slotgenerations so that the number of cuts made by the cutter during thefirst such generation is different than the number of cuts it makesduring the successive generation.

2. The method according to claim 1 wherein the alternation of the timedrelationship is made at least once during each successive cycle wherebythe number of cuts made by the blade during generation of any tooth slotdiffers from the number of such cuts made during generation of thepreceding slot.

3. The method according to claim 1 wherein at least three individuallydistinct timed relationships are utilized, respectively, duringsuccessive tooth-slot generations.

4. The method according to claim 1 wherein the cutting rate ismaintained at a constant value and alternation of the timed relationshipis achieved by changing the speed of the generating roll.

5. The method according to claim 3 wherein said intimed relation is madejust prior to each successive engagement of the cutter and blank, andcomprising the further step f. maintaining a predetermined constant timeinterval for the non-cutting steps of each repetitive cycle.

7. In a machine for cutting a multiple-tooth gear from a blank, of thetype having a repetitive cycle of machine movements for generating eachtooth slot, said cycle including a cutting portion in which the blank isengaged with a cutter during a generating roll of predetermined speed,the cutter being driven at a predetermined cutting rate in timedrelation to the roll to cut the blank a plurality of times during eachgenerating roll, the improvement comprising;

variation means responsive to machine movement during a portion of atleast one of said repetitive cycles for altering the timed relationshipbetween the cutting rate and the speed of the generating roll to changethe number of cuts made by the cutter during the second of twosuccessive generating rolls.

8. A machine according to claim 7 wherein said variation means isresponsive to said machine movement during a portion of each repetitivecycle to alter said timed relationship at least once during each cycle,whereby the number of cuts made by the cutter during any generating rollwill differ from the number of cuts made during the preceding generatingroll.

9. A machine according to claim 8 wherein said variation means includesrelationship selecting means adjustable to at least three conditionseach of which provides a respectively distinct timed relationshipbetween the cutting rate and generating roll, and

step means responsive to said machine movement at least once during eachrepetitive cycle for adjusting said selecting means to a different oneof said conditions during each cycle, whereby during at least threeconsecutive generating rolls three different timed relationships willoccur.

10. A machine according to claim 7 wherein said cutting rate ismaintained at a constant value and said variation means alters saidtimed relationship by changing the speed of said generating roll.

11. A machine according to claim 9 wherein said relationship selectingmeans includes a rotatable cam, and said step means includes a pawl andratchet.

12. A machine according to claim 9 wherein said selecting means isadjustable to at least four distinct conditions, and said step meansadjusts the selecting means to a predetermined sequence of timedrelationships, each one of said timed relationship being selected for arespective one of at least four consecutive generating rolls so that thenumber of cuts made during the third such roll is greater than thenumber of cuts made during the first roll and less than the number ofcuts made during the second roll, the latter cuts being less than thenumber of cuts made during the fourth such consecutive roll.

UNITED STATES PATENT @Filth CERTIFICATE OF CGRREQ'HQN Patent No. 3 653,-Z 0 Dated April 4 1972 Inventor-(s) Ernst J. Hunkeler It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Cancel columns 3 and4 and substitute the followings In its unloadedcondition cutter slide 24 which is slidable axially relative to cutterand cradle axes 20 and 26, is moved away from work head 10 (upward inFigG l) to permit a work blank 12 to be loaded and chucked in a spindle28 rotatably mounted within work head llLa The machine cycle is theninitiated, moving slide 24 toward work head 10 until cutter 14 is inposition to engagethe work blank 12, Cutter 14 is rotated at" apredetermined rate @out axis 20, and the generating roll is initiatedblank 12 being slowly rotated about axis 30 while cradle 22 slowlyrotates within slide 24 about its axis 26. This results in the wellknown generation of a spiral tooth slot in blank 12., During thisgenerating. roll, each blade 18 of cutter 14 makes at least one cutthrough the particular tooth slot being generated the number of suchcuts being predetermined by the timed relationship between the rate ofrotation of cutter l4 and the speed of the generating roll executed byworkpiece l2 and cradle 22E After the generating roll is complete,cutter slide 24 withdraws, and an appropriate indexing mechanism movesblank 12 into proper position to begin the cutting of the next sloto Themachine cycle then repeats itself until all of the tooth slots have beensuccessively generated in the blanks As indicated above, in all priorart gear generating machines the timed relationship between cutting rateand generating roll results in the generation of a particular cuttingpattern (Lee, a plurality of flat areas of varying width which comprisethe surface contour of each successive tooth slot). And due to thetooth-to tooth consistency of this timed relationship, the cuttingpattern is virtually identical on each of the gear teeth so generated;It is this repetitive cutting pattern which is one of the major sourcesof gear noise FORM uscoMM-oc 60376-F'69 n .5, GOVERNMENT PRINTING OFFICEI 1959 0-356-334,

Patent No. 3 ,6 S3 ,290 g l Page 2 peaks in power transmissions Theinvention herein avoids the generation of such identical cuttingpatterns, thereby obviating the noise problems which results from suchrepeating I cutting patterns This is accomplished by changing the timedrelationship between cutting rate and generating rolle,

As is known to those skilled in this art, the cutter on such generatingmachines maybe driven by an AC motor, while the repetitive machine cycleis often controlled by a DC motoro While it can be appreciated that avariation in the timed relationship between cutting rate and generatingroll can be achieved by changing the speed of either or both of thesemotors, according to the preferred embodiment of the invention hereinalteration of the timed relationship is achieved by changing the speedof the D6 motor during the generating roll The selective adjustment ofthe speed of thev DC motor is accomplished by the apparatus disclosed inFiga 20 The motior of cutter slide 24, as it brings the cutter intoposition to engage the work blank, moves a spning-=biased rod 32 whichcarries a pawl 34 in an upward direction as shown in Figc 2o Pawl 34 isbiased by a spring (not shown) into constant engagement with ratchetwheel 36 and, upon its upward moves-neat, turns ratchet wheel 36 onestep (30 in the embodiment shown) 0 This in turn rotates a cam 38 towhich ratchet wheel 36 is mechanically fixed by a common shaft 40.,

A cam follower 42 is biased by a spring 44 into constant engagement withthe surface of cam 38s Follower -42 pivots about axis 46 to drive geardwhich is fixed to follower 42 and also rotates about axis 460 Gear 48in turn drives gear 50 which is fixed to, positions; a shaft 52 of apotentiometer 54, The angular position of shaft 52, as detemined by cam38 through the drive mechanism just described above, selects variousvalues of resistance for potentiometer S4 in a well known manner?Potentiometer 543 inseifies electric circuit with machine cycle controlmotor 5 6 so that the resistance of potentiometer 54 determines therelative voltage drop appearing across motor 56 and thereby determinesthe speed of the latter as will be understood by those skilled in theart,

Following the generation of each successive tooth slot, cutter slide 24retracts (downward in Fig 2) being" followed by spring-biased rod 32which carries- 34 to. its lower position; After the work blank has beenindexed the repetitive cutting cycle begins once again with the forwardmovement of cutter slide 24G Pawl 3 5 then engages ratchet wheel 36 tostep Patent No, 3,653,290 Page 3 cam 38 to its next position, therebychanging the position of follower 42 and the setting of potentiometer 54to select a a different speed for motor 56 and alter the timed relationbetween cutting speed and generating rolla Figs 3 and 4 illustrate in asimplified, graphic manner the effect on tooth- -slot cutting patternsof variation in the timedrelationship between cutter rate and generatingrollo A cutter blade 18 is shown in each illustration in position readyto make a first cutting pass through a work blank 12. Therepresentations referred to by letters A=-D and A H indicaterespectively, the relative positions of the same cutter blade onsuccessive cutting passes through.

the blank in effecting the generation of similar tooth slots 58 and 58"Fig. 3 illustrates a timed relationship in which the speed of thegenerating roll ie relatively fast in com== parison to the rate ofrotation .of the cutter head. while Fig, 4 illustrates a timed relationin which the generating roll is relatively slow relative to the rotationof the cuttero As can be seen in the latteicase; each pass of a cutterblade through the slot cuts out much less metal than does each pass of acutter blade when the generating roll is relatively faster as shown inFig. 39 Because different amounts of metal are removed, the position andrelative size of the flat areas fwhich comprise the contour of the toothslot are different in each case,

. According to the preferred embodiment of the invention herein it iscontemplated that a plurality of different timed relationships will beused'in the cutting of any one particular gear, and Fig, 5 illustrates apossible sequence of twelve different timed relationships which might beselected by movement of cam 38 in response to each one of twelve 30steps-o The units (R) indicated on the ordinate are purely arbitrary andare not intended to indicate any actual resistances; generating rollspeeds or cuts per tooth slot, but only to show differences in the timedielationships and the relative direction of such diffferenteso In thisregard, attention is called to the preferred pattern of the timedrelationships suggested in Figo 5. When cutting successive tooth slotsaccording to this pattern, the motor speeds are varied to prevent anyrepetitive pattelc'nso That is, the number of cuts per slot do notincrease or v decrease in any regular manner For instance, during thefirst Patent No.. 3,653,290 I Page 4 four slot generations (using timedrelationships illustrated in Fig 5) the number of cuts 59C made duringthe third such generation exceeds the number of cuts 59A made during thefirst but is less than the cuts 5913 during the seccnd while generationof the fourth slot will require mere cuts 59!) than the secendo Ofcourse it will be understced that any number of different timedrelationships can used, In

the preferred forms of the invention, it is net csly suggested that thetimed relatienships be selected such that they do not repeat in aregular manner but, further, that the member of such timed relationshipsshcslld net be in any exact multiples of the number of teeth on thebeing generetedo Figo 6 is a simplified schematic :ef the circuitry usedfor energizing the cycle centi'el meter '56 acccrding to the inventionhereing Basically this citcuit comprises: a cam opereted switch t0,having an upper centect 62 and a lower contact 64;; petentiefneter 562which controls the speed cf the generating roll as abeve; and indexCOHiZZfG-l potentiometer 66 which is te centre-l the speed of themachine cycle during the retest; sterile the indexing of the workpiece&

Prior tc the generating roll and just befcre cutter slide 24 TRUVQSE thecutter 1H2 intc its engagement with the wet blank a timing cam (netsheen) HEGVGS switch 60 to the full line pesiticn illestrstedin Fig, 6that it closes with rapper centsct 62La this pet "ice the speed 01?meter 56 cent-relied. by the circuit inciudisc; petentiemetet 54,, thesetting cf potentiemeteit 54 being altered fer each generating r011 asdescribed in detail abeveo we a Signed and sealed this 20th day cf March31.9720

51 3s,": fittest:

EDWARD I LFLETCHER,JR. HUBER? GQTISCELALK Attesting Officer 7 vCemmissioner of Patents

1. In a method for cutting a multiple-tooth gear from a blank by using awell known repetitive cycle including the steps of: a. engaging a cutterwith the blank while producing a relative rolling motion therebetween ata predetermined speed to generate a tooth slot in the blank, and b.moving the cutter at a predetermined cutting rate in timed relationshipto said generating roll so that the cutter makes a plurality of cuts inthe blank during each generating roll, the improvement comprising thefurther step of: c. altering the timed relationship of the cutting raterelative to the speed of the generating roll between at least twosuccessive tooth slot generations so that the number of cuts made by thecutter during the first such generation is different than the number ofcuts it makes during the successive generation.
 2. The method accordingto claim 1 wherein the alternation of the timed relationship is made atleast once during each successive cycle whereby the number of cuts madeby the blade during generation of any tooth slot differs from the numberof such cuts made during generation of the preceding slot.
 3. The methodaccording to claim 1 wherein at least three individually distinct timedrelationships are utilized, respectively, during successive tooth-slotgenerations.
 4. The method according to claim 1 wherein the cutting rateis maintained at a constant value and alternation of the timedrelationship is achieved by changing the speed of the generating roll.5. The method according to claim 3 wherein said individually distincttimed relationships are selected sequentially so that, during fourconsecutive tooth-slot generations, the number of blade cuts made duringgeneration of the third such successively cut slot is greater than thecuts made during the generation of the first slot and less than thenumber of cuts during generation of the second slot, the latter beingless than the number of cuts made during generation of the fourthsuccessive slot.
 6. The method according to claim 4 wherein alterationof timed relation is made just prior to each successive engagement ofthe cutter and blank, and comprising the further step of: f. maintaininga predetermined constant time interval for the non-cutting steps of eachrepetitive cycle.
 7. In a machine for cutting a multiple-tooth gear froma blank, of the type having a repetitive cycle of machine movements forgenerating each tooth slot, said cycle including a cutting portion inwhich the blank is engaged with a cutter during a generating roll ofpredetermined speed, the cutter being driven at a predetermined cuttingrate in timed relation to the roll to cut the blank a plurality of timesduring each generating roll, the improvement comprising; variation meansresponsive to machine movement during a portion of at least one of saidrepetitive cycles for altering the timed relationship between thecutting rate and the speed of the generating roll to change the numberof cuts made by the cutter during the second of two successivegenerating rolls.
 8. A machine according to claim 7 wherein saidvariation means is responsive to said machine movement during a portionof each repetitive cycle to alter said timed relationship at least onceduring each cycle, whereby the number of cuts made by the cutter duringany generating roll will differ from the number of cuts made during thepreceding generating roll.
 9. A machine according to claim 8 whereinsaid variation means includes relationship selecting means adjustable toat least three conditions each of which provides a respectively distincttimed relationship between the cutting rate and generating roll, andstep means responsive to said machine movement at least once during eachrepetitive cycle for adjusting said selecting means to a different onEof said conditions during each cycle, whereby during at least threeconsecutive generating rolls three different timed relationships willoccur.
 10. A machine according to claim 7 wherein said cutting rate ismaintained at a constant value and said variation means alters saidtimed relationship by changing the speed of said generating roll.
 11. Amachine according to claim 9 wherein said relationship selecting meansincludes a rotatable cam, and said step means includes a pawl andratchet.
 12. A machine according to claim 9 wherein said selecting meansis adjustable to at least four distinct conditions, and said step meansadjusts the selecting means to a predetermined sequence of timedrelationships, each one of said timed relationship being selected for arespective one of at least four consecutive generating rolls so that thenumber of cuts made during the third such roll is greater than thenumber of cuts made during the first roll and less than the number ofcuts made during the second roll, the latter cuts being less than thenumber of cuts made during the fourth such consecutive roll.